motherload

Although you may dig a load of ore out of a mother lode, the spelling “motherload” is a mistake which is probably influenced by people thinking it means something like “the mother of all loads.” A “lode” was originally a stream of water, but by analogy it became a vein of metal ore. Miners of precious metals dream of finding a really rich vein, which they refer to as a “mother lode,” most often spelled as two words, though you also commonly see it spelled as one.